The number of echoes combined into a single image or image set in multiple echo imaging sequences or echo-train techniques such as rapid acquisition with relaxation enhancement (RARE), fast-spin echo (FSE), and turbo spin-echo (TSE). In RARE imaging, the ETL typically equals the acceleration factor.
As for tooth pain, it is caused by a reaction of the nerves inside a tooth's pulp chamber with the severity dependent upon the type and degree of the stimulus. What follows are some examples of symptoms you may be feeling and their possible causes.
Other causes of gum pain can be impaction, infection, tooth decay, cysts and pain due to pressure. 1  When the wisdom tooth doesnât fully grow but breaks out from the gums, the condition is called impacted tooth.  When an erupted wisdom tooth is covered with a flap of skin, gum infection like pericoronitis occurs.